[4] The amygdala has a primary role in the processing of memory, decision-making, and emotional responses (including fear, anxiety, and aggression).

[4][10] The basolateral complex is surrounded by the intercalated cell net that is inhibitory and projects to a broad variety of areas in the basal forebrain, hypothalamus, and the amygdala.

The right hemisphere is also linked to declarative memory, which consists of facts and information from previously experienced events and must be consciously recalled.

In contrast, stimulation of the left amygdala was able to induce either pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions.

Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development.

For the left amygdala, it is inferred that the early development of it functions to provide infants the ability to detect danger due to its reported responds predominantly to fearful events and faces.

[25][26] One study found evidence that, on average, women tend to retain stronger memories for emotional events than men.

[27] Variability in amygdala connectivity has been related to a variety of behaviors and outcomes such as fear recognition[28] and social network size.

[29] A simple view of the information processing through the amygdala follows as: the amygdala sends projections to the hypothalamus, septal nuclei and BNST (via the amygdalofugal tract), the dorsomedial thalamus (via the amygdalothalamic tract), the nuclei of the trigeminal nerve and the facial nerve, the ventral tegmental area, the locus coeruleus, and the laterodorsal tegmental nucleus.

[36] The lateral amygdalae, which send impulses to the rest of the basolateral complexes and to the centromedial nuclei, receive input from the sensory systems.

[8][9][37] In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events.

The association between stimuli and the aversive events they predict may be mediated by long-term potentiation,[38][39] a sustained enhancement of signaling between affected neurons.

[40] Accumulating evidence has suggested that multiple neuromodulators acting in the amygdala regulates the formation of emotional memories.

Exploring the primary attractive pheromone activates the basolateral amygdala and the shell of nucleus accumbens but neither the ventral tegmental area nor the orbitofrontal cortex.

In contrast, exploring the secondarily attractive male-derived odorants involves activation of a circuit that includes the basolateral amygdala, prefrontal cortex, and ventral tegmental area.

Experiments have shown that administration of stress hormones to mice immediately after they learn something enhances their retention when they are tested two days later.

[53] The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh.

[56] Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insula, during their practice.

[58] Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae.

As early as 1888, rhesus monkeys with a lesioned temporal cortex (including the amygdala) were observed to have significant social and emotional deficits.

[60] Heinrich Klüver and Paul Bucy later expanded upon this same observation by showing that large lesions to the anterior temporal lobe produced noticeable changes, including overreaction to all objects, hypoemotionality, loss of fear, hypersexuality, and hyperorality, a condition in which inappropriate objects are placed in the mouth.

Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them.

[69] The amygdala's role in the analysis of social situations stems specifically from its ability to identify and process changes in facial features.

[74] Recent studies have suggested possible correlations between brain structure, including differences in hemispheric ratios and connection patterns in the amygdala, and sexual orientation.

Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight-or-flight response.

[93] With advances in neuroimaging technology such as MRI, neuroscientists have made significant findings concerning the amygdala in the human brain.

A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders.

In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs (antidepressant medication) or psychotherapy.

[95] In 2006, researchers observed hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations.

[100][101] For people with manic bipolar I disorder, a decreased negative functional connectivity between the orbitofrontal cortex and the amygdala was also observed.